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How to Incremental Generate Makefile With Cmake?

6 minutes read

When using CMake, you can incrementally generate a makefile by running the CMake command with the -D option to specify additional variables or options. This allows you to make changes to your project or build configuration without having to regenerate the entire makefile from scratch.


For example, you can use the -D option to add new source files, change compiler flags, or modify build targets. This can save time and resources, especially for large projects with complex build configurations.


To incrementally generate a makefile with CMake, simply run the cmake command with the desired options and variables. This will update the existing makefile with the changes you have made, without regenerating everything from the beginning.


Overall, using the -D option in CMake allows for more flexibility and efficiency when working on projects with makefiles. It makes it easier to iterate on your build configuration and make adjustments as needed.


How to set up libraries in a CMake project?

  1. Create a folder for your libraries within your project directory. You can name this folder "libs" or any other name you prefer.
  2. Place your library source code files in this folder. This may include header files (.h, .hpp) and source files (.c, .cpp).
  3. In your CMakeLists.txt file, add the following lines to specify the location of your libraries folder and the libraries you want to build: 
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# Specify the location of libraries folder
set(LIBRARY_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/libs)

# Add library directory to the project
add_subdirectory(${LIBRARY_SOURCE_DIR})


  1. Create a CMakeLists.txt file within your libraries folder to define the build process for each library. This file should contain the necessary commands to build the library, such as setting include directories, adding source files, and creating a library target. Here is an example of what this file may look like:
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# Create a library target
add_library(my_library
    source_file1.cpp
    source_file2.cpp
)

# Specify include directories for the library
target_include_directories(my_library PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})


  1. Finally, in your main CMakeLists.txt file, link the libraries to your project by adding the following line:
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# Link libraries to the project
target_link_libraries(your_main_target my_library)


  1. Remember to run CMake to generate the build system files (e.g. Makefiles or Visual Studio project) and build your project to incorporate the libraries.


How to handle dependencies in a CMake project?

To handle dependencies in a CMake project, you can use the find_package() command to locate and import external libraries that your project depends on. Here are the steps to handle dependencies in a CMake project:

  1. Identify the dependencies that your project requires. This could be third-party libraries, packages, or modules that are not included in your project source code.
  2. Use the find_package() command in your CMakeLists.txt file to search for and import the necessary dependencies. For example, if your project requires the Boost library, you can use the following command to find and include Boost: find_package(Boost REQUIRED)
  3. Once the dependencies have been located, you can use the variables provided by find_package() to link the necessary libraries to your project. For example, you can use the ${Boost_LIBRARIES} variable to link the Boost libraries to your project: target_link_libraries(your_target ${Boost_LIBRARIES})
  4. Make sure to include any necessary include directories and definitions in your project configuration. You can use the ${Boost_INCLUDE_DIRS} variable to include the Boost headers in your project: target_include_directories(your_target PUBLIC ${Boost_INCLUDE_DIRS})
  5. Repeat this process for any additional dependencies that your project requires.


By following these steps, you can effectively handle dependencies in a CMake project and ensure that your project can build and run successfully with all required libraries and packages.


What is the role of find_package in CMake?

The find_package function in CMake is a way to locate and load configuration files for external software packages. It searches for a package in system-specific locations or user-specified directories, and then provides the necessary information for CMake to use the package in a project. This includes setting up appropriate include directories, library directories, and compiler flags.


find_package is commonly used to find libraries, such as Boost, OpenCV, or Qt, that are required by a CMake project. By using find_package, CMake makes it easier to manage dependencies and allows projects to be easily built on different systems without manually specifying the paths to external libraries.


How to generate makefile with CMake on Windows?

To generate a makefile with CMake on Windows, follow these steps:

  1. Create a new directory to store the makefile project.
  2. Open a command prompt and navigate to the directory you just created.
  3. Run the following command to generate a makefile using CMake: cmake -G "Unix Makefiles" Replace with the path to the directory containing your C/C++ source code files.
  4. After running the above command, CMake will generate the makefile in the same directory where your source code resides.
  5. To build the project using the generated makefile, run the following command: make
  6. If you want to clean the project, run: make clean


That's it! You have successfully generated a makefile using CMake on Windows.


What is the significance of cmake_modules in CMake?

CMake is an open-source cross-platform build system that is widely used in C++ projects to manage the build process. CMake modules refer to the scripts containing CMake functions and macros that can be used to extend the functionality of CMake.


The significance of cmake_modules in CMake lies in the ability to simplify and streamline the build process by providing reusable code that can be included in CMakeLists.txt files. These modules can contain functions and macros that help with tasks such as finding external libraries, setting compiler flags, locating include directories, and configuring project settings.


By using cmake_modules, developers can avoid duplicating code and save time by utilizing pre-written functionality. This modular approach also makes it easier to maintain and update the build system, as changes only need to be made in one central location.


Overall, cmake_modules are an essential part of CMake that helps developers manage complex build configurations and dependencies more efficiently.


How to incremental generate makefile with CMake while avoiding unnecessary recompilation?

To generate a makefile incrementally with CMake while avoiding unnecessary recompilation, you can follow these steps:

  1. Use the -DCMAKE_EXPORT_COMPILE_COMMANDS=ON flag when configuring your CMake project. This will generate a compile_commands.json file that contains information about each compilation unit in your project.
  2. Use the cmake --build . command to generate the makefile and compile the project. This will use the information in the compile_commands.json file to only recompile files that have changed or their dependencies have changed.
  3. Make sure to only modify files that are necessary for your changes. If you modify a file that is not used by any other files, it will not trigger a recompilation of other files.


By following these steps, you can incrementally generate a makefile with CMake while avoiding unnecessary recompilation. This can save you time during the development process and improve your overall build efficiency.

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